The invention relates to battery power-control and, more particularly, to battery monitoring.
Flashlights, handheld computers, and cellular telephones are not the only devices that are xe2x80x9cbattery-operated.xe2x80x9d Large-scale battery installations are used, for example, as backup power sources in the telecommunications industry and in uninterruptable power supplies. Because these applications are inherently reliability-sensitive (these are backup applications, after all), it is essential to monitor the state of such batteries. In order to thoroughly monitor the status of several cells within a battery, and several batteries within an installation, conventional battery monitoring systems may distribute sensors throughout the battery stacks and run several wires from each cell to a central battery monitor. The complex array of wires that results is not only inconvenient and expensive to install and maintain, it also poses a hazard to personnel and equipment. Some monitoring systems reduce the expense and hazard associated with such an installation by reducing the number of cells monitored, proportionally reducing the number of connecting wires strung to the central monitor. Although some cost savings and reduction in hazard may be achieved by this approach, there is a concomitant reduction in battery monitoring information. This dearth of battery information may lead to costly, otherwise avoidable, battery faults and can result in power outages and loss of service.
A system and method for monitoring a battery permits relatively easy interconnection of monitoring units and, at the same time, provides thorough monitoring of the battery components would therefore be highly desirable.
A battery-monitoring system in accordance with the principles of the present invention includes one or more cell sensor modules linked to a battery sensor module via a xe2x80x9cpower-isolatedxe2x80x9d network. In turn, one or more battery sensor modules may be linked to an alarm interface. A battery-monitoring system in accordance with the principles of the present invention may form a hierarchical system that includes one cell-sensor module per battery cell, with all the cell sensor modules linked to a battery sensor module and, in a multi-battery configuration, all the battery sensor modules linked to an alarm interface that provides access to the external world, in the form of a workstation that operates as a site monitor, for example.
Each cell sensor module may be configured to fit between the terminals of a cell and to attach to cell terminals via spring-clips and tabs. Each cell sensor module may include one or more sensors that sense a cell-related physical parameter, a signal conditioner, a controller, and a communications interface. The one or more sensors may be voltage or temperature sensors, for example, and the signal conditioner may include circuitry configured to amplify, offset, scale-adjust or otherwise enhance the raw signal provided by the one or more sensors. Additionally, the signal conditioner may include one or more analog-to-digital-converters (ADCs) configured to convert the conditioned sensor signals from the one or more sensors from analog to digital form. A single ADC with multiplexed input may be used to convert multiple sensor inputs, for example. The cell sensor module""s controller, which may take the form of an embedded microprocessor core within an application specific integrated circuit, for example, may initiate the conversion of sensor signals from analog to digital form and store the results of such conversions. The controller may also perform analytical operations, such as averaging values obtained by the sensors, determining peak sensor values, and logging events such as the excursion of a sensor signal beyond one or more thresholds. The controller may also exercise control over the communications interface, receiving messages from the interface and formatting responses through the interface. In order to ensure survivability of the communications link while, at the same time, employing a relatively simple, economical, serial topology, the communications link is xe2x80x9cpower-isolated.xe2x80x9d That is, the local and link sides of the interface employ separate power sources. The local side of each communications interface receives power from the cell to which the sensor module is attached and the link side of the communications interface receives power from a central source, such as the battery sensor module, for example. In this way, the failure of an individual battery cell will not xe2x80x9cbring downxe2x80x9d the entire communications network.
A battery sensor module may be configured to fit between a battery terminal and a load; attached, for example, to a bus bar that provides the conductive path from the battery to the electrical load. Each battery sensor module may include one or more sensors that sense a battery-related physical parameter, a signal conditioner, a controller, and a communications interface. The one or more sensors may be voltage, temperature, or current sensors, for example, and they are connected to measure corresponding battery-level values. That is, unlike a cell sensor module, which is configured to monitor the voltage, temperature or other parameter of an individual cell within a battery, a battery sensor module is configured to measure, for example, the voltage and discharge current, of the entire assemblage of cells that constitute a battery. The battery sensor module""s signal conditioner may include circuitry configured to amplify, offset, scale-adjust or otherwise enhance the raw signal provided by the one or more sensors. Additionally, the signal conditioner may include one or more ADCs configured to convert the conditioned sensor signals from analog to digital form. A single ADC with multiplexed input may be used to convert multiple sensor inputs. The battery sensor module""s controller, which may take the form of an embedded microprocessor core within an application specific integrated circuit, may initiate the conversion of sensor signals from analog to digital form and store the results of such conversions. The controller may also perform analytical operations, such as averaging values obtained by the sensors, determining peak sensor values, and logging events such as signal excursions beyond thresholds. The controller may also exercise control over the communications interface: receiving messages from the interface and formatting responses to the interface. The battery sensor module""s controller may query the various cell sensor modules within the battery, analyze sensor output and/or reduced data from the various cell sensor modules, and provide information to the alarm interface related to the status of the cells under its purview.
The alarm interface includes a communications interface for communicating with one or more battery sensor modules. The alarm interface provides a link between each cell and each battery in an installation and the external world. The external world may take the form, for example of a workstation that operates as a site monitor, for example. The alarm interface may include a user interface that permits input from and output to a user, directly, through visual and/or audio signals, or remotely, through a communications link.
In an illustrative embodiment, the isolated data interface includes opto-isolators at each cell sensor module and at the batter sensor module. The opto-isolators provide separation between the electrical power system of each cell sensor module and the electrical power system of the link, which obtains power from the battery sensor module. Additionally, in this illustrative embodiment, the topology of the battery cell communications link is a daisy-chained serial link, with its physical layer in compliance with the RS485 communications standard.
The new battery-monitoring system may be particularly useful in high-capacity battery installations, such as those employed in telecommunications systems and uninterruptable power supplies, for example. The new system is also useful in high-voltage mobile battery applications, such as hybrid electric vehicles (HEVs) which require precise monitoring and management but employ large high-voltage battery arrays.